Modal Dispersion Reduction in Multi-Mode Circular Dielectric Waveguides at W-band Frequencies

In multi-gigabit communication links using dielectric waveguides (DWGs) dispersion is a common cause of disturbances. The waveguide dispersion in circular dielectric waveguides can be minimized by a certain outer diameter for circular waveguides or a certain combination of inner and outer diameter of circular-hollow waveguides. A main disadvantage of using such waveguide-dispersion-optimized DWGs is their multi-mode guiding. In case that higher order modes are excited at the feeding transition or along the DWG, modal dispersion occurs and may reduce the data rate due to inter-symbol interference. In this paper a mode filter concept is presented that reduces the power of excited higher modes in circular multi-mode dielectric waveguides. The functionality of the filter is investigated and optimized by simulation. Finally, three different filter types are fabricated and the reduction of modal dispersion is verified by an impulse response analysis.